Topolearngrep is the fastest way to find where something is mentioned, in one file or across a whole project.
grep PATTERN [FILE...] prints every line containing a match for PATTERN. With no file it reads standard input, so it works at the end of any pipeline. Quote the pattern in single quotes so the shell leaves it alone.
The flags you'll use daily:
-iignore case;-vinvert: print lines that do not match.-nprefix line numbers;-cprint only the count of matching lines.-wmatch whole words only, so-w catskipsconcatenate.-llist only the names of files that contain a match.-rsearch a directory tree recursively (-Ralso follows symlinks).-e PATadds a pattern (repeatable, also needed for patterns starting with-).
When several files are searched, grep prefixes each line with the file name; -h hides it and -H forces it. With -r, narrow the search with --include='*.py', --exclude='*.min.js' and --exclude-dir=node_modules.
By default the pattern is a basic regular expression, so characters such as . and * are special. If you are searching for a literal string, use -F (fixed strings): it is faster and you can't be surprised by a stray dot.
Flags combine freely: grep -rniw todo src/ finds TODOs, any case, as whole words, with file names and line numbers.
Example
printf 'apple pie\nbanana split\nApple tart\ncherry pie\n' > menu.txt
grep apple menu.txt # apple pie
grep -i apple menu.txt # apple pie / Apple tart
grep -v pie menu.txt # banana split / Apple tart
grep -c pie menu.txt # 2
grep -n cherry menu.txt # 4:cherry pie
grep -F 'pie' menu.txt # literal search, no regex meaning
# recursive search in a project, only Python files, skipping a directory
grep -rn --include='*.py' --exclude-dir=.venv 'import requests' .
grep -rl 'TODO' src/ # just the file namesRemember
- -i ignore case, -v invert, -n line numbers, -c count, -w whole word
- -r searches directories; narrow it with --include and --exclude-dir
- -F treats the pattern as a plain string: faster and no regex surprises
Watch out for
- Forgetting to quote the pattern, so the shell expands * or splits words before grep sees them.